This invention relates to an improved process for preparing p-bromophenoxyacetaldehyde dialkylacetal derivatives.
The acetals are useful for synthetic intermediate of a substituted phenoxyalkylaminopyrimidine derivative (for example, Japanese Provisional Patent Publications No. 36667/1984 and No. 67/1987) which shows potent activity as an antiacaricide.
p-Bromophenoxyacetaldehyde dialkylacetal derivatives have heretofore been prepared by reacting p-bromophenols and chloroacetaldehyde dialkylacetals in the presence of a base (J. Argic. Food Chem., vol 36, p. 378 (1988), French Pat. No. 1,537,206 and Japanese Provisional Patent Publication No. 313743/1988). However, this method has disadvantages that (1) ortho-isomer and dibromo compound are formed with amounts of 20 to 30% when phenols being brominated and (2) the reaction rate is extremely slow.
The former disadvantage can be overcome only by recrystallization to obtain the pure para-isomer. Besides, in order to overcome the latter disadvantage of reaction rate, bromoaccetaldehyde dialkylacetals which are expensive and hardly obtainable in industry must be used in place of cheap chloroacetaldehyde dialkylacetal, and also as a solvent, amides such as dimethylformamide, which are easily decomposable should be used. The acetal substituent is generally extremely weak to acid, and it is decomposed in the condition of forming hydrogen bromide, so that a novel method which is to be replaced with the conventional method has been desired.